Mottled enamelware



Patented May 13, 1941 Eugene E.

Bryant, nectar-a,

Ohio, assignor to FerroEnamel Corporation, Cleveland, Ohio, a

corporation of Ohio No Drawing. Application November '1, 1938,

Serial No. 239,336

Claims.

This invention, as indicated, relates to mottled enamelware and a method of producing the same.

The term mottled, as used herein, is descriptive of a porcelain enamel coating possessing an irregular lacy pattern resulting from a surface ornamentation of the base metal over which the enamel is applied. The surface ornamentation most commonly resorted to in producing mottled ware is a controlled rusting of the ferrous base over which the protective enamel coating is applied.

It has been found that the controlled rusting of the metal base, in order to securethe mottled appearance, may be effected eitherprior to the application of the enamel or by means of a constituent in the wet enamel slip applied to the ware.

Irrespective of which procedure has been followed, a period up to about 24 hours has been required in order to effect a sufflcient amount of rusting of the work that the proper mottled appearance might be produced. It has, therefore, been common practice to incorporate the rusting agent in the enamel slip and to then very slowly dry the green work for a period of about 2 to 24 hours during which time the rusting constituent in the slip performs its function and at the end of which time the green and 'then dried work may be fired in a. m e to produce the fused enamel coating through which the pattern of the rusted surface of the work shows, in providing the mottled appearance of the latter.

There are two principal objections to this prior art procedure which is now commonly followed, in that enamels of high final gloss have not been adapted for use with such process and the long drying period of the green work has necessitated extra storage space and additional handling.

It is, therefore, a principal object of this invention to provide a method of producing a mottled appearing enamel surface without the'necessity of along drying period to allow the corrosive ma- A further object isto provide a method of obtaining a mottled appearing enamel surface of a high gloss. 1

Other objects of the invention will appear as the description proceeds. 7

To the accomplishment of the foregoing and related ends, said invention, then consists of the steps hereinafter fully described and particularly pointed out in the claims. The following descrip-' tion sets forth in detail one approved method of carrying out the invention, such disclosed method, however, constituting but one of the ways in which the principle of the invention may be employed.

In general, my invention comprises the discovery that afully satisfactory mottled appearance may be imparted in'a very short timeto the ferrous work surface, prior to the application of the enamel thereon, by the use of suitable reagents under properly controlled conditions so that the enamel, when applied to the work, may be immediately dried and flred and the entire process of producing mottled enamelware reduced to a substantialy continuous sequence of steps without the necessity of storing the work in order to develop the mottled appearance.

In general, my invention comprises the steps of treating the ferrous surface of the article to be enamelled with a selected corrosive solution under properly controlled temperature conditions for a predetermined length of time. passivating the surface after such treatment and then applying the enamel.

The process comprising my invention for mottling the ware is performed after the ware has been otherwise prepared as by pickling or acid treatment for the reception of the enamel coat. General care should be exercised to clean the ware prior to subjecting the same to the steps comprising my process for mottling, in particular, any excess acidor the like adhering to the work from the conventional pickling step should be rinsed or soaked therefrom.

The controlled rusting process forming a part of my invention may be performed either before or after the c tomary neutralizing step during which any acid remaining on the work and which mightinterfere with the successful application of enamel is neutralized by means of an alkali bath. I

To the ware thus properly pickled, and, as indicated, either before or after the neutralizing step, I apply a corrosive aqueous solution of a sulphate, preferably by dipping in the solution. The sulphate which is used may be either sodium sulphate, nickel sulphate or copper sulphate. If sodium sulphate is employed, the same may be added to the solution in the form of commercial Glaubers salt, since the impurities'in such com- -merclal material are not fOllIld that a rather close control over the concentration of the sulphate in the aqueous solution is necessary. When sodium sulphate is employed, an aqueous solution of 1% to 4% of the same will be found to produce most satisfactory results- When nickel sulphate is employed, an aqueous solution of from /z% to 3% will be found detrimental. I have such as NaCl, KCl,

Inasmuch as the mottled appearance of the work is due to the generation thereon. of an oxide film which film later combines with the enamel to produce the mottled effect, minor amounts of an oxidizing agent added to the solution will be found useful. xidizing agents such as potassium sulphide (potassium sulphuret) and sodium sulphide employed in amounts of about 1 to 2 ounces to 100 gallons of solution have been found to aid in the production of a heavy and thus more distinctive mottle. These alkali sulphides may be present in the form of a mixture of the various sulphides. Various other oxidizing agents may be employed such as potassium dichromate and potassium permanganate but the alkali sulphides above indicated will generally be preferred.

- I have found that in order to produce a mottled appearance of the desired "character and in the desired time, the pH of the corrosive solution should be rather carefully controlled. I have found that the pH of the corrosive aqueous solution employing any of the sulphates above mentioned should range from about 5 to 8 or sometimes 8.5 and generally from 6.5 to 7.5 for best results. Too low a pH valueproduces a rusting of such intensity that actually no mottle design is produced and when the pH value is too high, no mottle at all is produced. When sodium sulphate is employed, the preferable pH range is from 7 to 7.5. When nickel sulphate or copper sulphate is employed, the preferable pH range is from about '7 to about 8.

Various agents may be employed to regulate the pH of the solution such as sodium bicarbonate, ammonium hydroxide, and ammonium carbonate, of which sodium bicarbonate is preferred, since it sets up a buffer solution with the result that the pH value holds constant for a longer period'of time. When it is desired to use an agent such as ammonium carbonate, as when the corrosivesolution contains-nickel sulphate, a small amount of sodium bicarbonate may also be added as a buffer to aid in holding the pH value constant.

Any electrolyte that has a corrosive action on steel when in a solution adjusted; to a pH of from about 5 to 8.5 will produce the desired mottled effect but sulphates are generally preferred since their use seems to cause the least defects in the enamel surface. A mixture of sulphates, such as a mixture of sodium sulphate and nickel sulphate, gives excellent results. The chlorides CaClz, the nitrates, etc., whether added as such or produced in the bath by the addition of acids and pH control agents, will .be found to be satisfactory insofar as the production of a mottled surface is concerned but are generally less desirable'than the sulphates that a. certain amount of air is always mixed and circulated with the steam. The temperature may be maintained at any figure from room temperature up to about 250 F. and preferably film relied upon to produce the mottled design,

due to their tendency to adversely affect the enamel. Mixtures of chlorides and sulphates may also be employed with generally improved results over those obtained when the chlorides are employed alone.

From the corrosive solution the ware next passes to a steam closet where it is allowed; to

remain until the desired degree of mottling is obtained. Any moist or non-drying atmosphere greatly accelerates this rusting process which is also furthered by the application of heat. The use of steam provides an efi'ective and inexpensive method of afiording the proper conditions the ware should :be at a temperature approximately equal to that maintained in the closet and this necessitates heating the corrosive solution from which the ware passes to the steam closet. a

When corrosive solutions of the preferred concentrations and preferred pH are applied to the work andthe latter subjected to the substantially non-drying atmosphere maintained at the preferred temperature range, a very satisfactory mottle will be produced in from about 5 to 15 minutes. In this way, the step of mottling the work is reduced to the point where it may be performed while the ware passes practically continuously through a general plant for the produc tion of porcelain enamelled articles. No storage is necessary and, therefore, expensive storage facilities need not be provided and the expense of rehandling is eliminated.

-If the concentration of the corrosive solution is changed from the preferred ranges above given in order, for example, to produce a slightly different form of mottled appearance, the time required for the corrosive solution to act may be somewhat lengthened. In general, the best results will be produced by solutions which will act to produce the desired effect in a period not substantially in excess of 30 to" 45 minutes, and usually such desired result may be obtained in less than 15 minutes. Following the above treatment, the ware should be rinsed, first, in water and then in a neutralizer solution to remove any material harmful to enameling. The mottled surface may be passivated, usually by a mild alkali wash and then a rinse in clear water. After drying, the ware may then be enamelled by a normal procedure employing a, relatively clear enamel which will permit the mottle design to show through. Much clearer enamels and enamels with much higher gloss may be used than those generally applied in the past to make the usual gray or mottled ware sothat the finished ware is considerably improved in appearance. A color may be produced. whichis distinctly different from the ordinary gray. I

The enamel which is applied'over the mottled surface of the work prepared in accordance with the principles of my invention may be a substantially clear porcelain enamel of the following general formula:

The enamel, converted into a slip in accordance with conventional practice is-applied to of moisture and temperature, care being taken the mottled surface by conventional means such appearing enamelled surface is desired and is as dipping or spraying and the ware then fired not limited to the production of kitchenware at the usual temperatures as the last step in and the like. the complete process. Other modes of applying the principle of my The above described process may, as indl- 5 invention may be employed instead ofthe one cated, form a part of a substantially continuous explained, change being m s r rd the process for the production of mottled enamelled m h d here n disclosed, P v h p 1 ware, and the following is a brief outline of the steps s ed y any of t e ol o cla ms or various steps comprising such continuous process, the equivalent of such stated step or steps be The ware, as it is received from the forming e p 7 machines or presses, is racked in suitable baskets I, therefore, p r icul rly point out and disof the type usually employed in handling ware tinctly claim as my i v n i n of this character. The baskets of ware, unless -1. The method of producing a mottled appreviously degreased, are soaked in a cleaner pearing enamel surface which comprises coating tank to remove grease and dipped in a wash 5 the surface of a ferrous article tobe enamelled tank to remove the cleaning fluid. Then the with a corrosive solution of an electrolyte havbaskets of ware are immersed in a pickling soluing a pH ranging'from 5 to 8, maintaining said tion for the purpose of cleaning the surface surfacein a substantially moisture-saturated atthereof in order that the enamel may be properly mosph'ere .until a well-defined mottled surface is bo ded t e o- The Pickling SOhItiOn usually produced, rinsing and passivating the mottled c nt n amount of iron 111Dhate which, as surface coating the article with a vitreous enamel the basket is removed from the pickling tank, v u d t firing the enamel, will deposit a slight scum 0n the surface 0! the 2, The'method of producing a, mottled appear- Y Ware- I Order to em s c t e basket ing enamel surface which comprises coating the is next dipp i a mild acid rinse Which 35 surface of a ferrous article to be enamelled with moves all foreign material from the surface of a ossive solution of any electrolyte having a the ware. The baskets of ware are then preferpH ranging from 5 t 3, maintaining id y dipped in a wash tank for the purpose of face in a heated substantially moisture-saturated removing y c s ou of ac d ad er atmosphere for a period on the order of about to e At this P a is commonly five to about thirty minutes, rinsing and passikncwn s a nickel n tm t, may be used vating the mottled'surface coating the article to improve the bonding of the porcelain enamel. with a vitreou enamel slip and then firing the This treatment is followed by one or more wash enamel. tanks. It is, of course, necessary to passivate 3. The method of producing a mottled appearthe surface ofthe work before any enamel is 'ing enamel surface which comprises coating the pp eover, such P i g step a y surface of a ferrous article to be enamelled with compr i n l li Wa h f r he P p Of a corrosive solution of an electrolyte having a neutralizing the acid surface of the ware. The pH ranging from 6.5 to 7.5, maintaining said surnic tl ne step comp e feature of y face in a substantially moisture-saturated atvention may, as indicated, be performed either 40 mosphere at a temperature of \from about 150 before after this p ng step, but since a to 250 F. for a period of from five to fifteen r in mount of corrosion of the w re akes minutes until a well-defined mottled surface is place ur n the mettlihg p. I prefer to carry produced, rinsing and passivatlng the mottled on the various steps of the general p ess n surface coating the article with a vitreous enamel such sequence that the mottling step immediateslip and then firing the enamel.

y precedes final DaSSiVatiI-ig P- 4. The method of producing a mottled appeare mettiing p of t e general p e s 0 ing enamel surface which comprises coating the sists in dipping the baskets containing the surface of a ferrous article to be enamelled with cleaned ware as received from the above dea solution of corroding and oxidizing agents havscribed treatment into the mottling solution ing a pH ranging from 5 to 8, maintaining said and from this tank the baskets are then placed surface in a substantially moisture-saturated atin another tank, usually covered, in the bottom mosphere at a temperature of from about 150 of which is maintained a'water bath in order to t 185 F, with a well-defined mottled surface is provide the non-drying atmosphere within which produced, rinsing and passivating the mottled the w c o t produce the mottled surface coating the article with a vitreous enamel design. This tank has been referred to hereinslip and then firing the enamel. before as a steam closet. 5, The method of producing a mottled appear- The baskets of ware removed from the steam ing enamel surface' which comprises coating the closet are next immersed in passivating solutions urface 1 a, ferrous article to be enamelled with which m y e a clear Water rinse n a mild 0 a corrosive solution of sulphate having a pH alkaline rinse, and after being removed thereranging from 5 to 8, maintaining said surf from, the were is dried and 1S ady to be in a substantially moisture-saturated atmosenamelled; the enamelling step comprising either phere at a temperature of from about 150 to pp r pr y n the Wa e w h a slipof the 250 F. until a well-defined mottled surface ischaracter above defined after which the were is 5- produced, rinsing and passivating the mottled i ediately d ed a m y be promptly fi surface coating the article with a vitreous As above indicated, the principal advantage enamel slip and then firing the enamel.

- ve from e mploymen of the process of ,6. The method of producing a mottled appearthis invention is that the enamel does not reing enamel surfacewhich comprises coating the quire a long drying period and production is corsurface of a ferrous article to be enamelled with respondingly accelerated. Also, the improved a corrosive solution of a sulphate and an. alkali ---appearance 41f E finished product enlarges the sulphide having a pH ranging from 5 to 8, maindemand for this tyii'ofware. taining said surface in a substantially moisture- It is to be understood, of course, that'this saturated atmosphere at a temperature-of from process may be em loyed whenever a mottled about to250 If. for aperiod-not longer than one hour but until is produced, rinsing and passivating the mottled a well-defined mottled surface surface coating the article with a vitreous enamel slip and then firing the enamel.

7. The method ofproducing a mottled appearing enamel surface which comprises coating the surface of a ferrous article to be enamelled with a corrosive solution of sodium sulphate having a pH ranging from 5 to 8, maintaining said surface in a substantially moisture-saturated atmosphere at a temperature of from about 150 to 250 F. for a period not longer than one hour but until a well-defined mottled surface is produced, rinsing and passivating the mottled surface coating the article with a vitreous enamel slip andthen firing the enamel.

8. The method of producing a mottled appearing enamel surface which surface of a ferrous article to be enamelled with a corrosive solution of sodium sulphate having a pH ranging from about 6.5 to 7.5, maintaining said surface in a substantially moisture-saturated atmosphere at a temperature of from about 150 to 185 F. until a well-defined mottled surface is produced, rinsing and passivating the mottled surface coating the article with a vitreous enamel slip and then firing the enamel.

9. The method of producing a mottled appearingenamel surface which comprises coating the surface of a ferrous article to be enamelled with a corrosive solution of sodium sulphate having a pH ranging from 5 to 8, maintaining said surface in a substantially moisture-saturated atmosphere at a temperature of from about 150 to 185 F. for aperiod of from 5 to 15 minutes, rinsing and passivating the the article with a vitreous enamel lip and then firing the enamel.

10. The method of pearing enamel surface whichcomprises coating the surface of a ferrous article to be enamelled with a corrosive solution of sodium sulphate having a pH ranging from 5 to 8 and containing a minor amount of an oxidizing agent, maintaining said surface in a substantially moisturee saturated atmosphere at a temperature of from about 150 to 250 F. for a period not longer than one hour but until a well-defined mottled surface is produced, rinsing and passivating the mottled surface coating the article with a vitreous enamel slip and then firing the enamel.

11. .The method of producing a mottled appearing enamel surface which comprisescoating the surface of a ferrous article to be enamelled with a corrosivesolution of nickel sulphate having a pH ranging from -5 to 8, maintaining said surface in a substantially moisture-saturated atmosphere at a temperature of from about 150 to 250 F. until a well-deflned'mottled surface is ing a pH ranging from produced, rinsing and passivating' the mottled surface coating the article with a vitreous enamel slip and then firing the enamel.

12. The method of producing a mottled appearing enamel surface which comprises coating the surface of a. ferrous article to be enamelled with a corrosive solution of nickel sulphate havabout 6.5 to 7.5, maintaining said surface in a substantially moisturecomprises coating the i saturated atmosphere at a temperature of from about 150 to 185 15 minutes, rinsing and passivating the mottled surface coating the article with a vitreous enamel slip and then firing the enamel.

13. The method of producing a mottled appearing enamel surface which comprises coat- 7 ing the urface of a ferrous article to be enamelled with a corrosive solution of nickel sulphate having a pH ranging from about 6.5 to 7.5, and containing .a minor amount of potassium sulphide, maintaining said stu'face in a substantially moisture-saturated atmosphere at a temperature of from about 150 to 185 F. for a period of from ing the surface of a ferrous article to be enammottled surface coating producing a mottled apmaintaining said surface having a pH ranging from 5 to 8, maintaining said surface in a substantially moisture-saturated atmosphere at a temperature of from about to 250 F. until a we -defined mottled surface is produced, rinsing mottled surface coating vitreous enamel slip and then firing the enamel.

15. The method of producing a mottled appearing enamel surface which comprises coating the surface ofa ferrous article to be enamelled with a corrosive solution of copper sulphate having a pH ranging from about 6.5 to 7.5 and containing a minor amount of an oxidizing agent,

in a substantially moisture-saturated atmosphere at a temperature of from about 150 to F. for a period of from 5 to 15 minutes, rinsing and passivating the mottled surface coating the article with a vitreous enamel slip and thenfiring the enamel.

EUGENE E. BRYANT.

F. for a period of about 5 to 

